Wave signal translating arrangement



y 7, 1947. H. A. WHEELER 2,421,138

7 WAVE SIGNAL TRANSLATING' ARFANGEMENT Filed Jun 1, 1945 i To DecoderK12 |3- o PULSE- 9 O T|ME PULSE- E v MOI J U QE DELAY E. i- 55--OSCILLOSCOPE RECIEVER NETWORK LIMITER 0 o o 9 0 Jill 4 l8 (fiols)GAIN- CONTROL SYSTEM Volts INVENTOR. HAROLD A. WHEELER ATTORN Y PatentedMay 27, 1947 ZAZLBS WAVE SIGNAL TRAN SLATING ARRANGEMENT Harold A.Wheeler, Great Neck, N. Y., assignor, by mesne' assignments, toHazeltine Research, Inc, Chicago, 111., a corporation of IllinoisApplication June 1, 1945, Serial No. 597,037

9 Claims.

This invention is directed to wave-signal translating arrangements fortranslating pulse signals which may have one or more sloping edges.Although the invention is subject to a variety of applications, it isespecially suited for use ina radio-locating and direction-findingsystem of the type utilizing pulse-modulated signals and it will beparticularly described in that connection.

In one radio-locating and direction-finding system of the type underconsideration, the desired information is conveyed by means of a pulsesignal, coded in accordance with a prescribed coding schedule. Forexample, the coded signal may include a pair of pulse components,individually having a fixed duration and a time separation that isvariable in a code sequence. In the preferred system, the coded signalis received, shaped and passed on to a decoder unit which automaticallyderives the desired information by deciphering the received signal.

The coded signal is shaped, in the usual case, by means of aconventional limiter in which the received pulses are clipped off at apredetermined amplitude level. Such an arrangement performs the desiredwave-shaping function but is subject to an operating limitation whichmay be undesirable in certain installations. This limitation followsfrom the fact that variations in signal strength of the received signalcause variations in the slope of leading and trailing edges of the pulsecomponents. As a consequence, the ordinary limiter which operates at afixed amplitude level produces in its output circuit pulse signalshaving pulse widths that also vary in accordance with the receivedsignal strength. This becomes objectionable where the pulse widths ofthe code components of the received signal are significant.

Circuit arrangements for responding to the sloping edges of appliedpulse signals have already been proposed. In one prior arrangement acontrcl potential is derived, having a magnitude that varies with theslope of one edge of the applied signal. The potential is developedacross a conventional time-constant circuit and is used to control thegain of a receiver to maintain the amplitude of the signal deliveredtherefrom within a relatively narrow range fora wide range of receivedsignal intensities. Such control arrangements, while providing asuitable automatic-gain-control potential, are not effective to shapethe edges of the translated pulse signal as is required to avoid theaforementioned pulsewidth variations inherent in conventional limitingof pulse signals which have sloping edges.

It is an object of the present invention, therefore, to provide animproved wave-signal translating arrangement for translating pulsesignals which substantially avoids one or more of the aforementionedlimitations of prior arrangements.

It is another object of the invention to provide an improved wave-signaltranslating arrangement for translating a pulse signal which may have asloping edge and foreffectivelysuppressing the sloping edge.

It is a particular object of the invention to provide an improvedwave-signal translating arrangement for translating a pulse signal whichmay have sloping, leading and trailing edges and for deriving therefroma pulse signal having substantially vertical edges.

In accordance with the invention, a wave-signal translating arrangementfor translating a pulse signal which may have a sloping edge comprises acontrollable signal-translating channel for supplying the signal to autilizing device. The arrangement has means connected to the channel atone point and responsive to the sloping edge of the pulse signal forderiving a control potential. Also, means are provided for applying thecontrol potential to a succeeding point in the channel to interruptsignal translation at the succeeding point for an interval having aduration approximately equal to, and a substantial time coincidencewith, the occurrence of the sloping edge of the pulse signal at thesucceeding point, effectively to suppress the sloping edge in the signaltranslated through the channel.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

In the drawing, Fig. 1 represents a Wave-signal translating arrangementincluding the present invention in a preferred form, and Fig. 2comprises graphs utilized in explaining the operation of the Fig. 1arrangement.

Referring now more particularly to Fig. l, the wave-signal translatingarrangement there represented may be considered as the receiving unit ofa radio-locating anddirection-finding system. The arrangement comprisesan antenna-ground system Ill, H for intercepting pulse-modulateddirection-finding signals which may have sloping, leading and trailingedges. The antenna system Ill, l I is coupled to the input terminals ofa, controllable signal-translating channel through which receivedpulse-modulated signals are supplied to a utilizing device. This channelis provided by a pulse-modulated wave-signal receiver |2, a time-delaynetwork i3, a pulse amplifier and limiter I4, and an oscilloscope lconnected in cascade in the recited order. The receiver unit l2 mayconstitute any conventional well-known arrangement for receiving anddemodulating pulse-modulated signals, such as a receiver of thesuperheterodyne type. The pulse amplifier and limiter I4 may comprise anamplifying arrangement of any desired number of stages in at least oneof which applied pulse signals are shaped by clipping andamplitude-limiting actions. This may be accomplished by ad lusting theoperating potentials of the stage so as to translate only anintermediate amplitude range of an applied pulse signal, eliminating themaximum and minimum levels thereof by way of the well-knownanode-current saturation and anode-current cutoiT phenomena,respectively. The time-delay network 3 and oscilloscope I5 may be ofconventional constructions, the oscillos'cope preferably being of thecathode-ray type used to monitor the wave-signal translating arrangementunder consideration. The pulse-modulated signal obtained in the outputcircuit of limiter l4 may be applied to an automatic decoding unit (notshown), as indicated by arrow 5.

A gain-control system I! is coupled by way of conductors l8 and Hi tothe output circuit of receiver It. for controlling the gain of channel|2-| 5, inclusive. Preferably, the gain-control system is or the typewhich utilizes the quiescent or noise signal output of receiver IE tostabilize the receiver gain at a desired normal value. If desired,theremay also be associated with receiver |2 a pulse gain-control system ofthe type particularly described in copending application Serial No597,035, filed concurrently herewith in thename or Harold A. Wheeler andassigned to the same assignee as the present invention. Such a pulsegain-control system is insensitive to the quiescent signal output ofreceiver [2, that is to say, it is ineffective in the absence of areceived pulse-modulated signal. Upon receipt of such a signal, however,the pulse gain-control system responds rapidly to develop a controlpotential for materially reducing the gain of channel |2-| 5, inclusive,early in the duration of the received signah The condition of reducedgain endures for an interval slightly greater than the duration of thereceived pulse-modulated signal and is effective to suppress the efiectsof spurious or interfering signals which may be received along with acoded pulse-modulated signal, as particularly described in the copendingapplication. An output circuit of the noise gain-control system H iscoupled to a control input circuit of receiver l2 for applying controlpotentials to the receiver for the purpose of controlling its gain.

The signaltranslating arrangement has means, designated 20, connected tothe signal-translating channel at one point and responsive to thesloping edge of a received pulse-modulated signal for deriving a,control potential. For the illustrated embodiment where it is desired toeffect a shaping or correction of both the leading and trailing edges ofreceived pulse signals, this means comprises a differentiating circuitfor deriving a first pair of pulses having opposite polarities. Morespecifically, unit 20 includes an amplifier comprising a triode vacuumtube 2| having an anode impedance 22 and an equal cathode impedance 23arranged to provide a balanced output circuit for the amplifier;Acou'pling condenser 24 and leak resistor 25 in conjunction withconductors I8 and I9 connect the input circuit of tube 2| to one point,specifically the output circuit of receiver l2, of channel |2-|5,inclusive. A condenser 26 and resistor 21 coupled to the anode impedance22 of amplifier 2| constitute a first difierentiating circuit while a.condenser 28 and resistor 29 similarly connected to the cathodeimpedance 23 constitute a second differentiating circuit. Each suchcircuit is selected to have a time constant which is very much less thanthe slope time, that is, the duration of the slope portions of the pulsesignals applied to unit 20 from receiver |2.

A full-wave rectifier system is associated with the differentiatingcircuits for developing, from a first pair of pulses derived in thedifierentiating circuit, a second and corresponding pair of pulses whichindividually are of the same polarity. The rectifying system comprises afirst diode 3B coupled between resistor '27 and acoinmon load impedance3| and a second diode 32 coupled be tween resistor 29 and common loadimpedance 3|. A battery 3G or other potential source ap= pliesanamplitude delay bias to each diode 30 and 32, rendering the rectifiersystem unrespon sive to the quiescent signal translated in channel|2-|5, inclusive, in the absence of a received pulse-modulated signal. Aconnection 33 extending from the common load impedance 3| to a controlinput terminal of unit i l constitutes means for applying the pulses ofcontrol potential derived in unit '20 to such a succeeding point in thechannel as to interrupt signal translation thereat for an intervalapproximately equal to, and occurring in time coincidence with, theoccurrence of the edges of the pulse signal at this succeeding point tosuppress theeclges of the signal translated in channel |2-|5, inclusive.

While a transmitting unit is customarily associated with the arrangementrepresented in Fig. l. to complete the radio-locating anddirectionfinding system, the present invention may be clearly understoodfrom a consideration or the receiver portion only. For this reason there mainder of the direction-finding system has been omitted from thedrawing. The operation of the Fig, l arrangement is represented in partby the curves of Fig. 2. I

Curve A represents the signal output obtained from receiver 12 of thesignal-translating channel |2|5, inclusive. The low-amplitude signalportions designated S denote the quiescent sig-' nal output of thereceiver obtained in the absence of a received signal. This quiescentsignal is initiated by and represents inherent disturbances within thereceiver as, for example, thermal agitation noise, shot effect and thelike. Gain-control system H utilizes the quiescent 'sig nal output tostabilize the receiver gain and maintain the amplitude of its uiescentsignal at or below a preselected amplitude level. The pulse componentsP1 and P2 constitute a received direction-finding signal of thepulse-modulated type which has a duration T1. The time separation ofthese pulse components is coded in accordance with a prescribed codingschedule. Each of the pulse components P1 and P2 has sloping, leadingand trailing edges and an intermediate flat or plateau portion.

The signal of curve A is applied to unit '20, amplified in tube 2| anddifferentiated in the differentiating circuits associated with thebalanced output arrangement of tube 2|, The ,diifferentiated signal thusestablished across'resistor 2 9 has the wave form and polarity of curveB. It contains a pair of pulses of opposite polarity for each of thecode components P1 and P2. The positive-polarity pulse P3 of each pairis derived from the leading edge of one of the code components and has aduration t1 equal to that of the leading edge of the code component. Thenegative-polarity pulse P4. of each pair is derived from and has aduration t2 equal to that of the trailing edge of each of the codecomponents P1 and P2. The differentiated signal established acrossresistor 21 has an identical wave form but reversed polarity, a polarityreversal being obtained in translation of the signal of curve A throughtube 2| to its anode circuit.

Each of diodes 30 and 32 rectifies the pulses of negative polarityapplied to its cathode from resistor 21 or 29, developing across thecommon load'impedance 3! the signal of curve C. This signal also has apair of pulse components representing the sloping edges of each of thecode components P1 and P2 and of negative polarity. The first pulse P3of each such pair corresponds with the leading edge of one codecomponent and is obtained by way of diode 3!]. The alternate pulse P4 ofeach pair corresponds with the trailing edge of each code component andis derived through the alternate diode 32. The broken horizontal lines61 and e2 designate the amplitud delay bias applied to the diodes 3i!and 32. The delay bias is such that signal components of curve B whichlie between the bias levels, such as the quiescent signal components Sq,are not translated by the rectifier system and hence do not appear incurve C. The negative-polarity control I pulses of curve C are appliedas a pulse-modulated bias potential to a bias control circuit of pulseamplifier and limiter l l. Broken horizontal line e3 represents thecutoff level of unit 14, demonstrating that each of th control pulses P3and P4 is effective to bias the pulse amplifier and limiter toanode-current cutoff for intervals which correspond to the duration ofthe leading and trailing edges of code components P1 and P2.

In order to simplify the graphical representation, the curves of Fig. 2neglect the time-delay of network 13 and, additionally, neglect thedelay in deriving the control pulses of curve C. In practical circuitapplications some time delay is generally encountered in the derivationof the desired control pulses. Accordingly, the delay of network [3 isadjusted to acorresponding value so that the control pulses P3 and P4 ofcurve C block unit It and interrupt signal translation thereat duringspaced operating intervals which have a duration approximately equal to,and a substantial time coincidence with, the occurrence at unit H! ofthe leading and trailing edges respectively of the code components P1and P2. Therefore, the output signal of pulse amplifier and limiter Ithas the wave form of curve D. The code components P1 and P2 of curve Drepresent that portion of each of code components P1 and P2 of curve Athat is translated by unit I4 in view of the control established thereonby the control potential of curve C. Specifically, the control potentialof curve C, by blocking unit It during the intervals t1 and t2,suppresses or eliminates the sloping edges in the signal translated.Therefore, the code components P1 and P2 of curve D correspond with thatfraction of the flat or plateau portion of each component P1 and P2 thatoccurs within the limiting levels of limiter M, which levels arerepresented by horizontal lines E and F. The code components of curve Dhave a width that is independent of the limiting levels E and F sincethe sloping edges of the code components are not translated by unit Id.

The signal of curve D, in turn, is applied to the oscilloscope it: wherethe performance of the channel l2-l5, inclusive, may be determined byreproducing the wave form of curve D on the screen of a cathode-ray tubein well-known fashion. This output signal of the limiter l4 may also besupplied to the automatic decoder (not shown) wherein the codedinformation conveyed by means of the time separation of code componentsP1 and P2 is deciphered. Unit 20 which suppresses the sloping edges ofthe translated code components permits the limiting action of unit Hi tobe accomplished without effecting the pulse width of the code componentssupplied to the decoder. This assures improved operation of the decodingmechanism.

The broken-line curve portions of curve D represent the signal output ofa conventional limiter having the limiting levels shown by horizontallines E and F but operating upon the sloping portions of the codecomponents as well as the fiat or plateau portions thereof. It isevident that in such an arrangement the Width of the limited pulsesvaries in accordance with the slope of the leading and trailing edges ofthe code components as well as the limiting levels. This result isavoided by the inclusion of unit 20 in the signal-translatingarrangement of Fig. 1.

In the illustrated embodiment of the invention the control pulses ofcurve C derived at one point in channel I245, inclusive, are applied toa succeeding point in the channel so as to suppress both the leading andtrailing sloping edges from the signal translated. By omitting thefunction of either diode 39 or 32, the arrangement may be utilized tosuppress only one of the sloping edges of the pulse components wherethis operation should be desired. Also, the time-delay network i3 neednot necessarily take the form of a pure time-delay mechanism. Where asufficient number of stages are included in unit it, the time oftranslation therethrough may correspond with the delay of unit 25 inderiving the control pulses. In such a case connection 33 may be madedirectly with a particular stage of unit Hi wherein the sloping edges ofthe pulse signals occur in time coincidence with the control pulsesobtained from the rectifier system of unit 26 While there has beendescribed what is at present considered to be the preferred embodimentof this invention, it will be obvious to those skilled in the art thatVarious changes and modifications may be made therein without departingfrom the invention, and it is, therefore, aimed in the appended claimsto cover all such changes and modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. A wave-signal translating arrangement for translating a pulse signalwhich may have a sloping edge comprising, a controllablesignal-translating channel for supplying said signal to a utilizingdevice, means connected to said channel at one point and responsive tosaid sloping edge of said signal for deriving a control potential, and

means for applying said control potential to a succeeding point in saidchannel to interrupt signal translation at said succeeding point for aninterval having a duration approximately equal to and a substantial timecoincidence with the occurrence of said sloping edge of said signal atsaid succeeding. point efiectively' to: suppress said sloping edge inthesignal translated through. saidchanneh 2. A wave-signal translatingarrangement, for translating a pulsesignal vvhiclzl may have a sloping.edge comprising; a controllable. signal-trans:- lating channel forsupplying said signal to a utilizing device, meansincluding adiffierentiating circuit connected; to said. channel: at one point. andresponsive to said: sloping edge of said. signal for deriving. acontrol! potential,. and means for applying: said control potential to asucceedingpoint in said channel to interrupt signal translation at said;succeeding point for an interval a duration approximately equal to and.a. substantial time coincidence with the occurrence of said sloping edgeof said signal at said succeed:- ing; point edectivel-y' to suppresssaid sloping edge in the signal translated through said channel.

3. A wave-signal translating arrangement for translating a pulse signalwhich may have a sloping edge comprising, acontrollablesignaltranslating channel for supplying; said signal to autili-zingdevice, means connected to, said channel at one point and responsive tosaid sloping edge of said signal for deriving, a control potential,time-delaymea-ns. in said channel. connected between said one point anda succeeding point for delaying said signal between said points by aninterval corresponding to the time delay in. deriving said controlpotential, and means, for applying said control potential to saidsucceeding point to interrupt signal, translation thereat for aninterval having, a duration approximately equal to and asubstantial timecoincidence with the. occurrence of said sloping edge of said signal atsaid succeeding point effectively to suppress said sloping edge thesignal. translated through said channel.

4. A wave-signal translating arrangement for translating a pulse signal;which may have a. sloping edge comprising, a controllablesignaltranslating channel for supplying said signal to autilizingdevice; means connected to said channel at one point for differentiatingsaid signal. to derive a pulse of control potential having the sameduration as said sloping. edge, time-delay means in said channelconnected between said one point and a succeeding point, for delayingsaid signal between said, points by an interval corresponding to thetime delay in deriving said control potential, and means. for applying.said control potential tosaid succeeding point.- to. interrupt signaltranslation thereat for an interval. having a duration approximatelyequal to and a substantial time coincidence with the oc cur-rcnce ofsaid sloping edge of said signal at said succeeding point effectively tosuppress said sloping edge in the signal translated through saidchannel.

5. A wave-signal translating arrangement for translating a pulse signalwhich may have a sloping edge comprising, a controllablesignal-translating channel. for supplying said signal to a. utie lizingdevice, means connected to said channel at one point for difierentiatingand rectifying said signal to derive a pulse of unidirectional potentialhaving a predetermined polarity and having the same duration as saidsloping edge, time-dolay means in said channel connected between saidone point and a succeeding point for delaying said signal between saidpoints by an inter-- val corresponding to the time delay in derivingsaid control potential, and means for applying said control potentialto. said succeeding point:

to interrupt signal translation thereat for aninterval having a.duration approximately equalto and a substantial time coincidence withthe occurrence of said sloping edge of said signal at said succeedingpoint efiectively to suppress said sloping edge-in the signal translatedthrough said channel.

6'. A. wave-signal translating arrangement for translating a pulsesignal which may have sloping, leading and trailing edges comprising, acontrollable signal-translating channel for supplying said signal to autilizing device, means connected to said channel atone point andresponsive to each of said sloping, leading and trailing edges forderiving therefrom a pair of spaced pulses of control' potential havinga duration equal to that of said leading-and; trailing edgesrespectively, timedelay means.- in said channel connected between saidone point and: a. succeeding point for delaying said signal between saidpoints by an interval corresponding to. the time delay in deriving eachof said pulses of control potential, and means for applying said pair ofcontrol pulses to said succeeding point to interrupt signal translationthereat during spaced intervals. having a duration approximately equal.to and a substantial time coincidence with the occurrence at saidsucceeding pointofsaid leading and trailing edges respectively of saidsignal effectively to suppress said sloping edges in the signaltranslated through said channel.

7. A. wave-signal translating arrangement for translating: a.- pulse.signal which may have; slopns, leading. and trailing edges comprising, acontrollable signal-translating channel for supplying said signal to a.utilizing device, means connected to said channel at one point fordifferentiating said signal to derive a first pair of pulses havingopposite polarities and a duration equal to that of said leading andtrailing edges respectively, full-wave rectifying means for developingfrom said first pair of pulses a second and corresponding pair of pulsesof control potential individually having a given polarity, time-delaymeans in said channel connected between said one point and a succeedingpoint. for delaying said signal between said points. by an intervalcorresponding to; the time. delay in deriving each of said pulses ofcontrol potential, and means for applying said pair of control pulsesto. said succeeding point to interrupt signal translation thereat.during spaced intervals: having a duration approximately equal to and asubstantial time coincidence with the occurrence at said succeedingpoint. of said leading and trailing edges respectively of said signaleffectively to. suppress said sloping edges in the signal translatedthrough said channel.

8- A wave-signal translating arrangement for translating a pulse signalwhich may have a slopin edge comprising, a. controllable signal-trans,-lating channel for supplying said pulse signal to a utilizing device andefiective in the absence of said pulse signal to translate a quiescentsignal representing inherent disturbances within said translatingarrangement, means connected to said channel at one point andunresponsive to said quiescent. signal hut. responsive. to said slopinedge. of said pulse signal for deriving a control potential, and meansfor applying said control potential to asucceeding point in said channelto interrupt signal translation at said succeeding point for an intervalhaving a duration approximately equal toai-nd a sulo'stantial' timecoincidence with the occurrence of said sloping edge of said saidtime-delay network being effective to delay said pulse signal by aninterval corresponding to the time delay in deriving said controlpotential, and means for utilizing said control potential to bias saidpulse amplifier to cutoiT for an interval having a durationapproximately equal to and a substantial time coincidence with theoccurrence of said sloping edge of said signal at said succeedingamplifier effectively to suppress said sloping edge in the signaltranslated through said channel.

HAROLD A. WHEELER.

